Exhaust heat recovery apparatus

ABSTRACT

An exhaust heat recovery apparatus includes an evaporation unit, a condensation unit, an evaporation-side communication part and a condensation-side communication part. The evaporation unit is disposed in an exhaust gas passage through which an exhaust gas flows and performs heat exchange between the exhaust gas and an operation fluid flowing therein, thereby evaporating the operation fluid. The condensation unit is disposed in a coolant passage through which an engine coolant flows and performs heat exchange between the operation fluid and the engine coolant, thereby condensing the operation fluid. The evaporation-side communication part connects the evaporation unit and the condensation unit for introducing evaporated operation fluid to the condensation unit. The condensation-side communication part connects the condensation unit and the evaporation unit for introducing condensed operation fluid to the evaporation unit. The condensation-side communication part is provided with a throttle part.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-37482 filed on Feb. 19, 2007, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an exhaust heat recovery apparatus, which is used for a vehicle such as an automobile.

BACKGROUND OF THE INVENTION

It is known to recovery heat of exhaust gas discharged from an exhaust system of a vehicular engine using the principle of heat pipe and to use the recovered heat for other purposes such as for warming the engine. For example, Japanese Unexamined Patent Application Publication No. 62-268722 describes an exhaust heat recovery apparatus for heating an engine coolant using heat of an exhaust gas from an engine. Specifically, an evaporation unit that has heat pipes is disposed in an engine exhaust pipe through which the exhaust gas flows and a condensation unit that has heat pipes is disposed in an engine coolant circuit through which the engine coolant flows.

As another example, Japanese Unexamined Patent Application Publication No. 4-45393 describes a looped heat pipe heat exchanger. The disclosed heat exchanger includes a looped closed circulation passage filled with an internal heat-transfer fluid, an evaporation unit disposed on the circulation passage for evaporating the internal heat-transfer fluid therein by receiving external heat, and a condensation unit disposed on the circulation passage at a position higher than the evaporation unit for performing heat exchange between the evaporated internal heat-transfer fluid and an external heat-transfer fluid.

FIG. 6 shows an example of an exhaust heat recovery apparatus. In the exhaust heat recovery apparatus shown in FIG. 6, an evaporation unit J1 and a condensation unit J2, as heat exchanging units, are disposed adjacent to each other in a horizontal direction. Ends of heat pipes J3 of the evaporation and condensation units J1, J2 are coupled to headers (communication parts) J5, so that the heat pipes J3 of the evaporation unit J1 are in communication with the heat pipes J3 of the condensation unit J2 through the headers J5.

In such exhaust heat recovery apparatuses, the temperature of the engine coolant is immediately increased by recovering the heat of exhaust gas, especially, in a cold starting of the engine, such as in winter. Therefore, fuel efficiency and heating operation can be improved. On the other hand, in an engine high-load condition, such as in hot summer, it is necessary to restrict the recovery of the heat of the exhaust gas so as to avoid overheating of the engine.

For example, it is proposed to provide the exhaust heat recovery apparatus with a diaphragm-type valve unit for stopping the circulation of the operation fluid. The diaphragm-type valve unit is constructed of a diaphragm that is movable in response to the pressure of the operation fluid and a valve body that is driven by the diaphragm. The valve unit restricts the heat from being excessively recovered.

SUMMARY OF THE INVENTION

The present invention is made in view of the foregoing matter, and it is an object of the present invention to provide an exhaust heat recovery apparatus, which is capable of restricting excess recovery of heat with a simple structure.

According to an aspect of the present invention, an exhaust heat recovery apparatus includes an evaporation unit, a condensation unit, an evaporation-side communication part, a condensation-side communication part and a throttle part. The evaporation unit is to be disposed in an exhaust gas passage through which an exhaust gas exhausted from an engine flows, for performing heat exchange between the exhaust gas and an operation fluid flowing therein, thereby evaporating the operation fluid. The condensation unit is to be disposed in a coolant passage through which an engine coolant flows, for performing heat exchange between the engine coolant and the operation fluid that has been evaporated in the evaporation unit, thereby condensing the operation fluid. The evaporation-side communication part connects the evaporation unit and the condensation unit for introducing evaporated operation fluid from the evaporation unit to the condensation unit. The condensation-side communication part connects the condensation unit and the evaporation unit for introducing condensed operation fluid from the condensation unit to the evaporation unit. The throttle part is disposed in the condensation-side communication part.

The throttle part is configured to restrict an exhaust heat from being excessively recovered. Accordingly, the excess recovery of heat is restricted by a simple structure.

For example, the throttle part is constructed of a fixed throttle having an orifice. An upper limit of the quantity of heat recovered in the exhaust heat recovery apparatus can be determined by setting an opening degree of an orifice of the throttle part and the amount of operation fluid enclosed in the exhaust heat recovery apparatus.

As another example, the throttle part is provided by a variable throttle that is capable of varying an opening degree of an orifice through which the operation fluid in accordance with a temperature of the operation fluid.

According to a second aspect of the present invention, an exhaust heat recovery apparatus includes an evaporation unit, a condensation unit, an evaporation-side communication part, a condensation-side communication part. The evaporation unit is to be disposed in an exhaust gas passage through which an exhaust gas flows, for performing heat exchange between the exhaust gas and an operation fluid flowing therein, thereby evaporating the operation fluid. The condensation unit is to be disposed in a coolant passage through which an engine coolant flows, for performing heat exchange between the engine coolant and the operation fluid that has been evaporated in the evaporation unit, thereby condensing the operation fluid. The evaporation-side communication part connects the evaporation unit and the condensation unit and defines a passage for introducing the operation fluid from the evaporation unit to the condensation unit. The condensation-side communication part connects the condensation unit and the evaporation unit, and defines a passage for introducing the operation fluid from the condensation unit to the evaporation unit. The condensation-side communication part includes a throttle portion that has a reduced passage area.

Accordingly, the excess recovery of heat is restricted by partly reducing the passage area of the condensation-side communication part.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic cross-sectional view of an exhaust heat recovery apparatus according to a first embodiment of the present invention;

FIGS. 2A and 2B are conceptual views for showing operations of an exhaust heat recovery apparatus as an comparative example;

FIGS. 2C and 2D are conceptual views for showing operations of the exhaust heat recovery apparatus according to the first embodiment;

FIG. 3A is an enlarged schematic cross-sectional view of an evaporation-side communication part of a exhaust heat recovery apparatus, in an operation fluid low-temperature condition, according to a second embodiment of the present invention;

FIG. 3B is an enlarged schematic cross-sectional view of the evaporation-side communication part of the exhaust heat recovery apparatus, in an operation fluid high-temperature condition, according to the second embodiment of the present invention;

FIG. 4 is an enlarged schematic cross-sectional view of a condensation-side communication part of an exhaust heat recovery apparatus according to a third embodiment of the present invention;

FIG. 5 is an enlarged schematic cross-sectional view of a condensation-side communication part of an exhaust heat recovery apparatus according to another embodiment of the present invention; and

FIG. 6 is a schematic cross-sectional view of an exhaust heat recovery apparatus of a related art.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

Referring to FIG. 1, an exhaust heat recovery apparatus of a first embodiment of the present invention is employed in a vehicle that is driven by an engine (e.g., internal combustion engine), for recovering exhaust heat of an exhaust gas from an exhaust system of the engine and using the heat for facilitating an engine warming up or the like.

The exhaust heat recovery apparatus generally includes an evaporation unit 1 and a condensation unit 2. The evaporation unit 1 is disposed in a first housing 100 that is in communication with an exhaust gas passage (not shown) through which the exhaust gas exhausted from the engine flows. In the present embodiment, for example, the first housing 100 is disposed in an exhaust pipe through which the exhaust gas flows. The evaporation unit 1 performs heat exchange between the exhaust gas and an operation fluid flowing therein, thereby to evaporate the operation fluid.

The condensation unit 2 is disposed outside of the exhaust pipe. The condensation unit 2 is disposed in a second housing 200 that is in communication with a coolant passage (not shown) of the engine, through which an engine coolant flows. The condensation unit 2 performs heat exchange between the operation fluid that has been evaporated in the evaporation unit 1 and the engine coolant, thereby to condense the operation fluid. The second housing 200 has a coolant inlet port 201 and a coolant outlet port 202. The coolant inlet port 201 is coupled to the coolant passage at a position downstream of the engine for introducing the coolant into the second housing 200. The coolant outlet port 202 is coupled to the coolant passage at a position upstream of the engine for introducing the coolant from the second housing 200 to the coolant passage.

In the present embodiment, for example, the first housing 100 and the second housing 200 are disposed adjacent to each other. Also, a clearance is provided between the first housing 100 and the second housing 200.

The evaporation unit 1 has a plurality of evaporation-side heat pipes 3 a and evaporation-side fins 4 a joined to outer surfaces of the heat pipes 3 a. The fins 4 a are, for example, corrugate fins. Each of the heat pipes 3 a has a generally flat tubular shape. The heat pipe 3 a is orientated such that its longitudinal axis extends in a vertical direction V, such as, an up and down direction in FIG. 1. Also, the heat pipe 3 a is orientated such that a major axis of a cross-section defined in a direction perpendicular to the longitudinal axis of the pipe 3 a is substantially parallel to a flow direction of the exhaust gas, such as in a direction perpendicular to a paper surface of FIG. 1. The heat pipes 3 a are stacked parallel to each other in a pipe stacking direction H, such as in a horizontal direction.

The evaporation unit 1 has evaporation-side headers 5 a at both ends of the heat pipes 3 a. The headers 5 a extend in the pipe stacking direction H to be in communication with all the heat pipes 3 a. One of the headers 5 a, which is in communication with upper ends of the heat pipes 3 a, is referred to as a first evaporation-side header 51 a, and the other header 5 a, which is in communication with lower ends of the heat pipes 3 a, is referred to as a second evaporation-side header 52 a.

The condensation unit 2 includes condensations-side heat pipes 3 b and condensation-side fins 4 b joined to outer surfaces of the heat pipes 3 b. The fins 4 b are, for example, corrugate fins. The heat pipes 3 b are generally flat tubes. Each of the heat pipes 3 b is orientated such that its longitudinal axis extends in the vertical direction V, such as, in the up and down direction in FIG. 1. Also, the heat pipe 3 b is orientated such that a major axis of a cross-section defined in a direction perpendicular to the longitudinal axis of the pipe 3 b is substantially parallel to the flow direction of the exhaust gas of the evaporation unit 1, such as in the direction perpendicular to the paper surface of FIG. 1. The heat pipes 3 b are stacked parallel to each other in the pipe stacking direction H, such as in the horizontal direction.

The condensation unit 2 includes condensation-side headers 5 b at both ends of the heat pipes 3 b. The headers 5 b extend in the pipe stacking direction H to be in communication with all the heat pipes 3 b. One of the headers 5 b, which is in communication with upper ends of the heat pipes 3 b, is referred to as a first condensation-side header 51 b, and the other header 5 b, which is in communication with lower ends of the heat pipes 3 b, is referred to as a second condensation-side header 52 b.

The evaporation-side headers 5 a are in communication with the condensation-side headers 5 b through communication parts 6, which have substantially tubular shapes. Thus, a closed, looped path is formed by the heat pipes 3 a, 3 b, the headers 5 a, 5 b and the communication parts 6. The path is filled with the operation fluid that is capable of being evaporated and condensed, such as water, alcohol or the like. The operation fluid circulates through the evaporation unit 1 and the condensation unit 2.

One of the communication parts 6, which is located on an upper side and connects the first evaporation-side header 51 a and the first condensation-side header 51 b, is referred to as a evaporation-side communication part 61. The operation fluid that has been evaporated in the evaporation unit 1 is introduced to the condensation unit 2 through the evaporation-side communication part 61.

The other communication part 6, which is located on a lower side and connects the second evaporation-side header 52 a and the second condensation-side header 52 b, is referred to as a condensation-side communication part 62. The operation fluid that has been condensed in the condensation unit 2 is introduced to the evaporation unit 1 through the condensation-side communication part 62.

The condensation-side communication part 62 has a fixed throttle 7 a as a throttle part. In the present embodiment, a throttle member 70 is disposed in the condensation-side communication part 62, and the fixed throttle 7 a is provided by the throttle member 70. That is, the throttle member 70 is disposed such that a passage area (e.g., a cross-sectional area) of a passage through which the condensed operation fluid flows is partly reduced in the condensation-side communication part 62.

The throttle member 70 forms an orifice having a reduced cross-section. For example, the throttle member 70 has a shape so that a cross-sectional area of the orifice gradually reduces from an upstream end toward a middle portion and gradually increases from the middle portion toward a downstream end, with respect to the flow of the condensed operation fluid. The throttle member 70 has a first tapered tubular wall 701 whose inner diameter reduces from an upstream position toward a downstream position with respect to the flow of the operation fluid, and a second tapered tubular wall 702 continuously extends from a downstream end of the first tapered tubular wall 702. An inner diameter of the second tapered tubular wall 702 increases from an upstream position toward a downstream position with respect to the flow of the operation fluid.

Next, an operation of the exhaust heat recovery apparatus will be described. FIGS. 2A and 2B are conceptual views for showing operations of an exhaust heat recovery apparatus without having a throttle part as a comparative example. FIGS. 2C and 2D are conceptual views for showing operations of the exhaust heat recovery apparatus of the present embodiment.

FIGS. 2A and 2C show conditions where the quantity Qin of heat of the exhaust gas introduced in the exhaust heat recovery apparatus is a first value Q1. FIGS. 2B and 2D show conditions where the quantity Qin of heat of the exhaust gas is a second value Q2 that is greater than the first value Q1. In FIGS. 2A to 2D, the plurality of evaporation-side heat pipes 3 a is simply illustrated by a singe heat pipe 3 a, for convenience of explanation. Likewise, the plurality of condensation-side heat pipes 3 b is simply illustrated by a single heat pipe 3 b. Further, the illustration of the fins 4 a, 4 b and the first and second housings 100, 200 are omitted in FIGS. 2A to 2D.

The operation fluid evaporated in the evaporation unit 1 flows in the condensation unit 2 through the evaporation-side communication part 61. In the condensation unit 2, the operation fluid is condensed and liquefied. The liquefied operation fluid flows in the evaporation unit 1 through the condensation-side communication part 62.

Due to the balance of the evaporation of the operation fluid in the evaporation unit 1 and the condensation of the operation fluid in the condensation unit 2, a water level difference h of the operation fluid is generated between the evaporation unit 1 and the condensation unit 2. The operation fluid is returned to the evaporation unit 1 from the condensation unit 2 due to the water level difference h. In this way, the operation fluid is circulated in the exhaust heat recovery apparatus.

In the exhaust heat recovery apparatus shown in FIG. 2A, pressure loss ΔP1 of a return flow of the operation fluid and the water level difference h satisfy the following relation:

ΔP1=ρgh

In the above equation, p denotes the density of the operation fluid in a liquid phase, and g denotes the gravitational acceleration. Here, the density p of the operation fluid and the gravitational acceleration g are constant. Thus, when the quantity Qin of the heat of the exhaust gas is constant, the water level difference h is determined by the pressure loss ΔP1. Qout denotes the quantity of heat transferred to the coolant in the condensation unit 2.

As shown in FIG. 2B, when the quantity Qin of the heat of the exhaust gas increases, the amount of the return flow of the operation fluid increases. With this, the flow speed of the operation fluid increases. Therefore, the pressure loss AΔP1 of the return flow of the operation fluid increases, and hence the water level difference h increases.

In the present embodiment shown in FIG. 2C, since the condensation-side communication part 62 is provided with the fixed throttle 7 a, pressure loss ΔP′ of the return flow of the operation fluid is determined by the sum of the pressure loss ΔP1 and pressure loss ΔP2 due to the fixed throttle 7 a (i.e., ΔP′=ΔP1+ΔP2). In this case, a water level difference h2 between the evaporation unit 1 and the condensation unit 2 is greater than the water level difference h of the exhaust heat recovery apparatus shown in FIG. 2A by the amount of the pressure loss ΔP2 of the fixed throttle 7 a.

Then, when the quantity Qin of the heat of the exhaust gas increases as shown in FIG. 2D, the pressure loss ΔP′ of the return flow of the operation fluid increases. With this, the water level difference h2, which is necessary for returning the operation fluid, is increased. When it becomes difficult to keep the water level difference h2 necessary for returning the operation fluid, the amount of the operation fluid returned to the evaporation unit 1 is limited. Thus, the quantity of heat recovered in the exhaust heat recovery apparatus plateaus.

In the present embodiment, the fixed throttle 7 a is provided in the condensation-side communication part 62. The upper limit of the quantity of heat recovered in the exhaust heat recovery apparatus is determined by previously setting an opening degree of the fixed throttle 7 a, such as the passage area of the orifice of the fixed throttle 7 a, and the amount of the operation fluid filled in the exhaust heat recovery apparatus.

Thus, the structure for restricting the excess heat recovery is simplified, as compared with an exhaust heat recovery apparatus having a diaphragm-type valve unit constructed of a diaphragm, a valve body and the like. (Second embodiment) A second embodiment of the present invention will be described with reference to FIGS. 3A and 3B. Components similar to the first embodiment will be designated by the same reference numerals, and a description thereof is not repeated.

In the second embodiment, the condensation-side communication part 62 is provided with a variable throttle 7 b as the throttle part, in place of the fixed throttle 7 a of the first embodiment. The variable throttle 7 b is configured to vary the opening degree of an orifice defined therein, that is, the cross-sectional area of the passage of the operation fluid, in accordance with the temperature of the operation fluid.

FIG. 3A shows a condition of the variable throttle 7 b when the temperature of the operation fluid is low, and FIG. 3B shows a condition of the variable throttle 7 b when the temperature of the operation fluid is high. The variable throttle 7 b is configured such that the opening degree is reduced in accordance with an increase in the temperature of the operation fluid.

In the present embodiment, the variable throttle 7 b is made of a material that is deformable in accordance with the ambient temperature. For example, the material of the variable throttle 7 b can be a bi-metal, a shape-memory alloy, or the like. Further, in the present embodiment, the variable throttle 7 b is configured such that the passage of the operation fluid is not fully closed, even when the temperature of the operation fluid flowing through the condensation-side communication part 62 is increased.

Next, an operation of the exhaust heat recovery apparatus of the second embodiment will be described. When the quantity Qin of the heat of the exhaust gas increases, the quantity of heat recovered in the exhaust heat recovery apparatus increases. In the present embodiment, the variable throttle 7 b is provided in the condensation-side communication part 62. When the quantity Qin of the heat of the exhaust gas increases, the temperature of the operation fluid increases. Thus, the opening degree of the variable throttle 7 b reduces with the increase of the temperature of the operation fluid, and hence the pressure loss ΔP2 increases. As such, an increase in the quantity of the heat recovered in the exhaust heat recovery apparatus is limited at a certain point. When the quantity Qin of the heat of the exhaust gas further increases, the opening degree of the variable throttle 7 b further reduces, and hence the pressure loss ΔP2 further increases. As a result, the amount of the return flow of the operation fluid reduces, and thus the quantity of heat recovered in the exhaust heat recovery apparatus reduces.

In the present embodiment, the condensation-side communication part 62 is provided with the variable throttle 7 b that varies the opening degree in accordance with the increase in the temperature of the operation fluid. Therefore, the quantity of heat recovered in the exhaust heat recovery apparatus is reduced in accordance with the increase in temperature of the operation fluid. Because the quantity of heat recovered in the exhaust heat recovery apparatus is limited when an engine load is high, such as in summer, in which the temperature of the operation fluid is high, it is less likely that the engine will be overheated.

Third Embodiment

A third embodiment of the present invention will be described with reference to FIG. 4. Components similar to the first embodiment will be designated by the same reference numerals, and a description thereof is not repeated.

As shown in FIG. 4, the exhaust heat recovery apparatus of the present embodiment has a variable throttle 7 c in the condensation-side communication part 62, as the throttle part. The variable throttle 7 c includes an orifice 71, a valve body 72 for opening and closing the orifice 71, and a temperature sensitive deformable member 73. An end of the deformable member 73 is connected to an end wall of the vale body 72 on a side opposite to the orifice 71. An opposite end of the deformable member 73 is connected to a support member 74 that is disposed in the condensation-side communication part 62.

The deformable member 73 is deformable in response to the temperature. For example, the deformable member 73 is configured to be thermally expanded when the temperature of the operation fluid passing through the condensation-side communication part 62 exceeds a predetermined temperature. The deformable member 73 is, for example, made of thermo-wax, thermo-metal, or the like, which has a coefficient of thermal expansion greater than that of the metal of the condensation-side communication part 62.

When the temperature of the operation fluid passing through the condensation-side communication part 62 increases, the valve body 72 is moved in a direction to reduce the opening degree of the orifice 71. On the other hand, when the temperature of the operation fluid passing through the condensation-side communication part 62 reduces, the valve body 72 is moved in a direction to increase the opening degree of the orifice 71. In the present embodiment, the valve body 72 does not fully close the orifice 71, even when the temperature of the operation fluid passing through the condensation-side communication part 62 is increased.

Since the condensation-side communication part 62 is provided with the variable throttle 7 c that varies the opening degree of the orifice 71 in accordance with the increase in the temperature of the operation fluid, the quantity of heat recovered in the exhaust heat recovery apparatus is reduced in accordance with the increase in temperature of the operation fluid. As such, the effects similar to the second embodiment will be provided.

Other Embodiments

In the first embodiment, the throttle member 70 forms the orifice the inner diameter of which gradually reduces from the upstream position toward the middle position and gradually increases from the middle position toward the downstream position with respect to the flow of the operation fluid. However, the shape of the orifice of the throttle member 70 is not limited to the above. For example, the throttle member 70 may have a cylindrical shape and may have a substantially constant passage area.

In the first embodiment, the fixed throttle 7 a is provided by the throttle member 70. However, the fixed throttle 7 a can be formed by partly reducing a passage area (e.g., inner diameter) of the condensation-side communication part 62, as shown in FIG. 5. In this case, the number of components is reduced. Further, the pressure loss ΔP2 of the fixed throttle 7 a is determined by arranging an inner diameter d and a length L of the fixed throttle 7 a.

In the second and third embodiments, the variable throttles 7 b, 7 c are disposed to directly contact the operation fluid, and the opening degrees of the variable throttles 7 b, 7 c are mechanically controlled in accordance with the temperature of the operation fluid. Alternatively, a temperature sensor can be separately employed to detect the temperature of the operation fluid passing through the condensation-side communication part 62, and the variable throttle 7 b, 7 c can be configured such that the opening degrees thereof are electrically controlled based on the temperature detected by the temperature sensor.

In the above embodiments, the condensation-side communication part 62 is exemplarily orientated horizontally. However, the orientation of the condensation-side communication part 62 is not limited to the above. The condensation-side communication part 62 can be inclined relative to a horizontal direction.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader term is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. An exhaust heat recovery apparatus comprising: an evaporation unit to be disposed in an exhaust gas passage through which an exhaust gas exhausted. from an engine flows, for performing heat exchange between the exhaust gas and an operation fluid flowing therein, thereby evaporating the operation fluid; a condensation unit to be disposed in a coolant passage through which an engine coolant flows, for performing heat exchange between the engine coolant and the operation fluid that has been evaporated in the evaporation unit, thereby condensing the operation fluid; an evaporation-side communication part connecting the evaporation unit and the condensation unit for introducing the operation fluid from the evaporation unit to the condensation unit; a condensation-side communication part connecting the condensation unit and the evaporation unit for introducing the operation fluid from the condensation unit to the evaporation unit; and a throttle part disposed in the condensation-side communication part.
 2. The exhaust heat recovery apparatus according to claim 1, wherein the throttle part includes a fixed throttle.
 3. The exhaust heat recovery apparatus according to claim 2, wherein the fixed throttle is provided by partly reducing a passage area of the condensation- side communication part.
 4. The exhaust heat recovery apparatus according to claim 1, wherein the throttle part includes a variable throttle that is configured to vary an opening degree of an orifice through which the operation fluid flows in accordance with a temperature of the operation fluid.
 5. The exhaust heat recovery apparatus according to claim 4, wherein the variable throttle is configured such that the opening degree is reduced in accordance with an increase in the temperature of the operation fluid.
 6. An exhaust heat recovery apparatus comprising: an evaporation unit to be disposed in an exhaust gas passage through which an exhaust gas exhausted from an engine flows, for performing heat exchange between the exhaust gas and an operation fluid flowing therein, thereby evaporating the operation fluid; a condensation unit to be disposed in a coolant passage through which an engine coolant flows, for performing heat exchange between the engine coolant and the operation fluid that has been evaporated in the evaporation unit, thereby condensing the operation fluid; an evaporation-side communication part connecting the evaporation unit and the condensation unit and defines a passage for introducing the operation fluid from the evaporation unit to the condensation unit; and a condensation-side communication part connecting the condensation unit and the evaporation unit and defines a passage for introducing the operation fluid from the condensation unit to the evaporation unit, wherein the condensation-side communication part includes a throttle portion that has a reduced passage area. 